1. Field of the Invention
The present invention relates to a composite valve and it particularly relates to a composite valve, provided with a main valve and a sub-valve in a common body, which is driven by a single solenoid.
2. Description of the Related Art
An automotive air conditioner generally includes a compressor, a condenser, an expander, an evaporator, and so forth. Here, the compressor discharges a high-temperature and high-pressure gaseous refrigerant produced by compressing a refrigerant flowing through a refrigeration cycle of a vehicle. The condenser condenses the gaseous refrigerant. The expander produces a low-temperature and low-pressure refrigerant by adiabatically expanding the condensed liquid refrigerant. The evaporator evaporates the refrigerant and thereby causes a heat exchange of the refrigerant with air inside a vehicle's compartment. The refrigerant evaporated by the evaporator is again brought back to the compressor and thus circulates through the refrigeration cycle.
The compressor is, for example, a variable displacement compressor (hereinafter referred to simply as “compressor” also) capable of varying the refrigerant discharging capacity in order to maintain a constant level of cooling capacity irrespective of the engine speed. This compressor has a piston for compression linked to a wobble plate that is mounted to a rotational shaft driven by an engine, and the compressor regulates the refrigerant discharge rate by changing the stroke of the piston through changes in the angle of the wobble plate. The angle of the wobble plate can be changed continuously by changing the balance of pressure working on both faces of the piston as part of the discharged refrigerant is introduced into an airtight crankcase. The pressure within this crankcase (hereinafter referred to as “crank pressure”) Pc is controlled by a control valve for a variable displacement compressor (hereinafter referred to simply as “control valve” also), which is provided between the discharge chamber of the compressor and the crankcase.
Such a control valve regulates the valve opening degree by supplying the externally applied current to a solenoid, which functions as a driver part. Suppose that an air conditioning function needs to be quickly fulfilled at the startup or the like of the air conditioner. Then, a valve section is set to a closed state by supplying the maximum current to the solenoid, for instance. Also, the wobble plate is tilt relative to the rotational shaft for a large angle by lowering a crank pressure Pc. As a result, the compressor can be operated at the maximum capacity. When the engine load of a vehicle is high, the compressor can be operated at the minimum capacity by fully opening the valve section with the solenoid turned off and by setting the wobble plate substantially at a right angle to the rotational shaft with the crank pressure Pc set high.
The control valve like this is disclosed in Reference (1) in the following Related Art List, for instance. That is, the control valve is provided with a main valve in a main passage that communicates the discharge chamber with the crankcase and also a sub-valve in a sub-passage that communicates the crankcase with the suction chamber. And the main valve and the sub-valve are driven by a single solenoid. During a steady operation, this control valve regulates the opening degree of the main valve with the sub-valve closed. Thereby, the crank pressure Pc can be controlled and the discharging capacity can also be controlled as described above. On the other hand, at a power-on of the air conditioner, the sub-valve is open with the main valve closed. Thereby, the crank pressure Pc is quickly lowered. As a result, the compressor can promptly shift its operation mode to a maximum-capacity operation. Also, a plurality of valves are opened and closed by the use of a single solenoid. Thus, the control valve can be of a reduced size as a whole.
In such a control valve as described above, the main valve and sub-valve are driven by the single solenoid. Thus, a main valve element and a sub-valve element are provided along the same axis line, and the control valve has a mechanism that transports the solenoidal force to the each valve element by way of an actuating rod provided along said axis line. The body of the control valve has a main valve hole, and the main valve element has a sub-valve hole. That is, the sub-passage runs through the main valve element. The main valve element touches and leaves a main valve seat, provided in an opening end of the main valve hole, so as to close and open the main valve, respectively. And the sub-valve element touches and leaves a sub-valve seat, provided in an opening end of the sub-valve hole, so as to close and open the sub-valve, respectively. Since, however, the sub-valve is pressed against the sub-valve seat by the biasing force of a spring during a steady operation of the compressor, the sub-valve is kept closed. At the startup of the compressor, the solenoidal force is at its maximum and the sub-valve element is further biased in a valve opening direction while the main valve element is seated on the main valve seat. This opens the sub-valve.